The invention relates in general to removing noise signals that reduce the quality of surface images constructed by a measuring instrument such as a scanning probe microscope (SPM). In particular, the invention relates to improving the quality of signals generated by a scanning tunneling microscope (STM), where the features of a surface are being measured on an atomic scale in the presence of vibration that affects the distance between the sample and probe.
The development of the STM in 1981 (see G. Binning, H. Rohrer, C. Gerber, and E. Weibel, Phys. Rev. Lett. 49, 57 (1982); Phys. Rev. Lett. 40, 178 (1982); Physica 109/110 b, 2075 (1982)) spawned the invention of a family of SPMs (see R. Wiesendanger, "Scanning Probe Microscopy and Spectroscopy", Cambridge University Press, 1994), which makes use of numerous interactions between a measuring probe and a material surface. Devices and structures which are investigated by SPM techniques have become increasingly smaller.
For SPM resolutions on an atomic scale, precise probe control and superior vibration isolation are necessary to obtain high fidelity signals. For example, to obtain a vertical resolution of 0.01 .ANG. in an STM requires a stability of the tip-to-sample spacing at the level of 0.001 .ANG. in conventional STMs. Therefore, vibration isolation is paramount for the successful operation of an STM or other measuring apparatus where high resolution is required.
Numerous studies have investigated ways to lessen the effects of vibration while making measurements and the theories of feedback and vibration isolation for SPMs in general. These studies have focused on damping systems for vibration isolation where the sources of vibration are external to the compartment in which the measurement is being made. For example, S. Park and C. F. Quate, Rev. Sci. Instrum. 58 (11), 2004, (1987) investigated several models of vibration isolation, one of which uses a spring and magnetic damping system as shown in FIG. 1, which is typical for SPMs.
In FIG. 1, the measuring tip and the sample under investigation are contained in box 50. The spring 52 and magnetic damper 54 function to reduce vibration of the box 50. It is the displacement, x, that Park and Quate sought to minimize. However, it is the uncontrolled variations of the displacement between the tip and the sample, which occurs inside the box 50, that degrades the image of the sample features. The uncontrolled variations of the displacement between the tip and the sample is typically caused by vibrations.
Most STM systems employ spring supports and magnetic damping as shown in FIG. 1. Some STMs are even floated on air tables and isolated from accompanying apparatus, such as molecular beam epitaxy machines, so they can resolve surface features on an atomic scale. The present invention eliminates such extreme measures for vibration isolation so that SPM measurements can be made with atomic resolution. The present invention allows more rugged SPMs (a class to which STM belongs) to be built that, for example, can be taken from laboratories for use in field tests where vibration would render a conventional SPM useless.